I bought the smallest amount Dharma sold, a couple of years ago, for a few small projects. But I still have a big bag left, and I don't know what to do with it.

I could keep it around, but I am uncomfortable with chemicals in a home with children, if they don't need to be there, or end up sitting around and forgotten about until unfortunately rediscovered one day.

Can I just throw it in the trash? Or do I need to dispose of it in a special way? How toxic is it, anyway. I have been searching online for 20 minutes now and haven't come up with much to answer these questions. I figured you all might know.

WASTE DISPOSAL METHODS (DISPOSER MUST COMPLY WITH FEDERAL, STATE AND LOCAL DISPOSAL OR DISCHARGE LAWS):
If permitted by applicable disposal regulations, bury in a sold waste landfill or dissolve and neutralize as follows: Dissolve in water using caution as
solution can get hot. Neutralize with acid and flush to sewer with plenty of water. Good ventilation is required during neutralization due to release of
CO2 gas. Neutralized waste may have to be disposed of by an approved contractor.

I will assume that you are asking about discarding soda ash (sodium carbonate) at home or in a teaching lab or art studio, not the large quantities that may be produced industrially.

If you are discarding small quantities that have been dissolved in water, it is safe to just pour it down the sink. Laundry detergent commonly contains quite a lot of sodium carbonate.

The high pH produced by a large amount of sodium carbonate might be bad for a septic system. Add enough vinegar (which is typically 5% acetic acid) or other acid to reach a neutral pH. USe pH paper to determine when you have added sufficient vinegar that your pH gets near 7, which is neutral. The pH of a strong solution of sodium carbonate may be as high as 12.

Once the pH has been neutralized, you will essentially have rather dilute salt water. This is fine for disposal in septic tanks or sewage systems, but should not be dumped directly on plants, as salt can be bad for plant growth.